Periodic DFT investigation of the effect of aluminium content on the properties of the acid zeolite H-FER

Grajciar, Lukáš; Areán, C. Otero; Pulido, Angeles; Nachtigall, Petr

doi:10.1039/b917969k

Cited by 51 publications

(61 citation statements)

References 81 publications

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“…For the sake of comparison with other computational studies [45][46][47][48][49][50][86][87][88] where the PBE [73,74] functional was adopted, additional calculations were performed employing the PBE1PBE [75] functional. Such a modified version of the PBE functional includes a 25% of HartreeFock exchange and was chosen in order to get results comparable at the same time to those obtained by the pure PBE and by the hybrid B3LYP functionals.…”

Section: Basis Set Effects On Cu ? Coordinationmentioning

confidence: 99%

“…The main challenge related to the application of quantum mechanical calculations is to find a compromise between accuracy and computational costs, taking into account that zeolites are complex solids with large unit cells. The most simple and the most complex computational approaches are, respectively, quantum mechanical calculations on small and nonstructure-specific cluster models [36][37][38][39][40][41], or the application of quantum-mechanical methods (mostly based on planewaves DFT) to the full periodicity of the zeolite lattice [42][43][44][45][46][47][48][49][50]. Apart from the above two extreme cases, the most widely employed approaches are nowadays molecular orbital calculations which treat only a portion of the S. Morpurgo (&) Á G. Moretti Á M. Bossa Dipartimento di Chimica, Università degli Studi di Roma ''La Sapienza'', P.le Aldo Moro 5, 00185 Rome, Italy e-mail: simone.morpurgo@uniroma1.it structure (i.e., the active site for a given reaction) taking into account in a variable way the geometrical constraints imposed by the remaining part of the crystal [51,52].…”

Section: Introductionmentioning

confidence: 99%

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Basis set effects on Cu(I) coordination in Cu-ZSM-5: a computational study

2012

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DFT calculations on the coordination of Cu+ to the framework oxygen atoms of Al-substituted ZSM-5 were performed by using combinations of different basis sets in order to investigate the dependence of the results on the adopted computational level. With low-end basis sets, a large basis set superposition error (BSSE) favors the coordination of Cu+ to three to four oxygen atoms of the framework, only two of which belong to the AlO4 tetrahedron corresponding to the investigated T-site. More extended basis sets considerably lower the BSSE and favor the coordination of Cu+ to only two oxygen atoms of the AlO4 tetrahedron. Upon interaction with NO, the Cu+ ion is always coordinated by two oxygen atoms of the AlO4 tetrahedron, independently of the basis set adopted and of the coordination number before NO adsorption. The shift from three-to twofold coordination caused by the Cu+-NO interaction requires a deformation energy that lowers the final adsorption energy. Such an effect is relevant with low-end basis sets, whereas it is substantially absent with more extended basis sets, which favor the twofold coordination of Cu+ even before NO adsorption. As a result, high-end basis sets increase the NO interaction energy with respect to that calculated by low-end basis sets, in agreement with experiments and suggesting a possible re-interpretation of the catalytic properties of the investigated sites. Provided suitable scale factors are employed, the N-O stretching frequencies of adsorbed nitrogen oxide calculated by sufficiently extended basis sets turned out in fair agreement with experimental findings

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Section: Basis Set Effects On Cu ? Coordinationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Basis set effects on Cu(I) coordination in Cu-ZSM-5: a computational study

2012

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“…Refs. [31][32][33][34][35][36]). These papers discuss substantial differences and important factors of zeolite acidity including (i) location of aluminum in zeolites, (ii) effects of Si/Al ratio, (iii) distance of Al atoms from each other, and (iv) role of the zeolite structure itself.…”

Section: Introductionmentioning

confidence: 97%

Aromatic Transformations Over Mesoporous ZSM-5: Advantages and Disadvantages

et al. 2010

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Catalytic behavior of mesoporous ZSM-5 was investigated in toluene disproportionation, toluene alkylation with isopropyl alcohol, and p-xylene alkylation with isopropyl alcohol to understand the effect of the presence of mesopores. Three ZSM-5 zeolites (conventional one and two mesoporous differing in the mesopore volume) having similar Si/Al ratio were synthesized and characterized as for their acidity (internal and external) as well as their micropore/mesopore volume. No substantial differences among three samples were observed as for the type and concentration of Brønsted and Lewis acid sites as well as their location in zeolite channels or on external surface of zeolite crystals. Conversions of toluene and p-xylene increased with increasing volume of mesopores in ZSM-5 zeolite while the selectivity to individual products depended on the type of reaction. In general, selectivity to sum of xylenes in toluene disproportionation, sum of isopropyltoluenes in toluene alkylation and to 1-isopropyl-2, 5-dimethylbenzene in p-xylene alkylation increased due to a shorter contact time molecules spent in mesoporous ZSM-5 catalysts. In contrast, para-selectivity decreased as diffusion pathways were shorten due to the presence of mesopores.

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“…Among several techniques used to the characterization of acidic properties of zeolites, FTIR spectroscopy is one of the most frequently used and useful for determination of the type, strength and concentration of acid sites of zeolites using different basic probe molecules and the results can be related also to theoretical calculations [17][18][19][20][21]. It is useful not only for evaluation the concentration of the acid sites of Lewis and Brønsted types but also for characterization and description of the types of hydroxyl groups [22].…”

Section: Introductionmentioning

confidence: 98%

TUN, IMF and -SVR Zeolites; Synthesis, Properties and Acidity

2010

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The effect of synthesis conditions on the preparation and properties of three novel zeolites TUN, IMF, and -SVR was investigated and compared with MFI. X-ray powder diffraction, infrared spectroscopy, chemical analysis, sorption measurements, and scanning electron microscopy were employed to characterize the textural and chemical properties of these zeolites. FTIR spectroscopy in combination with pyridine as probe molecule was used to describe the type, concentration and acid strength of these zeolites. Zeolite -SVR was synthesized with Si/Al ratios higher than 100 in contrast with TUN and IMF having Si/ Al ratios about 20-30, respectively. TUN, MFI and IMF zeolites exhibit similar concentrations of Brønsted and Lewis acid sites and also similar acid strength of Brønsted sites. In contrast, the presence of one vacancy/unit cell in the case of -SVR zeolite substantially changes its acidic properties. Generally, zeolites TUN and IMF exhibit similar acidic properties in terms of acid strength and Brønsted to Lewis acid site ratio like MFI and due to their slightly larger pores higher activities in catalytic reactions are expected.

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Periodic DFT investigation of the effect of aluminium content on the properties of the acid zeolite H-FER

Cited by 51 publications

References 81 publications

Basis set effects on Cu(I) coordination in Cu-ZSM-5: a computational study

Basis set effects on Cu(I) coordination in Cu-ZSM-5: a computational study

Aromatic Transformations Over Mesoporous ZSM-5: Advantages and Disadvantages

TUN, IMF and -SVR Zeolites; Synthesis, Properties and Acidity

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